The recent discovery that many cancers are generated by small fractions cancer stem cells (CSC) suggests that targets of effective new treatments might be found among the mutations that initiate and maintain these cells. Ependymomas include a diverse group of tumors that arise throughout the central nervous system (CNS) of children and adults. These tumors often resist conventional treatments and are incurable in up to 40% of patients. Therefore, to identify potential new therapeutic approaches for ependymoma, we sort to identify the cell(s) of origin of this disease and the mutations that transform these into CSC. By comparing the gene expression profiles of tumors with those of the developing nervous system, we found that ependymomas from the different parts of the CNS share the gene expression profiles of neural precursor cells, termed radial glia (RG), in the corresponding region of the embryonic nervous system. We showed also that ependymomas are propagated and maintained by CSC that are remarkably similar to RG and that ependymomas from the different parts of the CNS contain anatomic site-specific chromosomal alterations. Thus, we hypothesize that RG in the different parts of the CNS are cells of origin of ependymoma and are predisposed to acquire distinct gene mutations that transform these cells into ependymoma CSC. To test our hypothesis we propose a series of highly-integrated genomic and CSC studies that will employ mouse models and the largest cohort of human ependymoma tumors collated to date. We propose to: 1) Use the 500K single nucleotide polymorphism mapping array profiles that we have generated already from 230 samples of ependymoma to identify candidate oncogenes and tumor suppressor genes (TSG) of this disease. 2) Activate candidate oncogenes and knock-down candidate TSG in RG from the different regions of the CNS to determine if these cells are susceptible to be transformed into CSC. Assessment of CSC properties will include unbridled self-renewal and tumor initiating capacity. 3) Engineer in RG of a genetic mouse model, concurrent activation of Notchl signaling and Ink4a/Arf deletion that we have observed in human intracranial ependymoma. Relevance to Public Health: There is a desperate need for effective new treatments of ependymoma. By defining the cell of origin of ependymoma and the mutations that transform these cells, the Aims of this proposal will bring about a profound increase in understanding of this disease and identify molecular targets for new treatments.